After prolonged production pumping of oil wells, the crude oil sometimes becomes so thick and cumbersome that it is not possible to produce any further oil from the well. Under these conditions, it is common practice to "rejuvenate" the well by pumping hot steam under high pressure down the well pipestring and out into the formations. This hot steam will loosen up the thick crude oil and thin the oil out sufficiently that production pumping can be resumed.
In the actual rejuvenation process, the well pipestring is provided with a packing close to its lower end to confine the hot steam pumped down the pipestring to the lower annulus of the well so that the steam is forced out into the formations through the well casing perforations. Steam pressure is maintained for a considerable length of time in order that proper rejuvenation can take place. For example, once the steam has been forced down, it is necessary to maintain the pressure for anywhere from 3-5 days or wait a sufficient length of time for the steam to cool and the pressure to gradually diminish before a production pump can be lowered to resume pumping operations.
In an effort to avoid such delays, it has been proposed to keep the production pump in place in the pipestring and inject the steam down through the pump into the formations. However, this has proved to be unsuccessful because of gutting and damage to the pump itself by the hot steam.
As a consequence, in remedial well operations, it is still normally necessary to delay for a considerable length of time for the steam to cool and the pressure to drop before the production pump can be lowered into the well to resume operations.